1. Field of the Invention
The present invention relates to a lens for a vehicular lamp and to a manufacturing method for the same. More particularly, the present invention relates to a technique for preventing a vehicular lamp having a lens, in which plastic molded parts respectively having two or more colors are integrally formed, from mixing the color of one of the plastic molded parts with another one of the colors.
2. Description of the Related Art
There has been a vehicular lamp provided with a lens in which plastic molded parts respectively having two or more colors are integrally formed. A plastic lens has often been used as the lens of the vehicular lamp. Especially, a multicolor molded lens, in which plural plastic parts having different colors are integrally formed by performing what is called a multicolor molding method, has been used as a marker light. Thus, in the manufacture of a multifunction marker lamp constituted by combining marker lamps having different functions with one another, the process of molding a lens has been simplified. Also, parts-management has been simplified. Consequently, these have contributed to reduced cost.
Meanwhile, a conventional multicolor molded lens has been molded by using plural plastics, which are of the same kind and have similar physical properties and different colors, so as to improve the integration of plural plastic molded portions.
Thus, the conventional lens has a problem that the color of one of the plastic molded portions is mixed with the color of one of the plastic molded portions respectively having the other colors. In a case where there is a difference in depth between or among the colors of the plastic portions, when the portion which is lighter in color is post-molded, the above-mentioned problem is occurred, for example, the combination of red and amber portions, or the combination of red, amber, and clear (or colorless transparent) portions. In other words, in a case where the portion, which is deeper in color, is earlier injected (or pre-molded), and where the plastic portion, which is lighter in color, is then injected by leaving the plastic molded portion, which is deeper in color, in a mold, heat of the post-molded plastic portion is transmitted to the pre-molded plastic portion. At this time, the pre-molded plastic portion is dragged by the post-molded plastic portion. Thus, a phenomenon, in which the color of the pre-molded plastic portion is mixed with that of the post-molded plastic portion, that is, what is called color mixture is caused.
Further, for instance, in the lens of a vehicular marker lamp, the clear portion is often post-molded as a collecting-side resin so as to integrate the plural portions. For instance, in a case where a lens having three plastic molded portions, that is, red, amber, and clear plastic molded portions is molded, the red portion and the amber portion are molded at a first injection-molding step. The clear portion is molded at a second step. Then, the clear portion is formed integrally with the red portion and the amber portion. Consequently, a lens, in which the red portion, the amber portion, and the clear portion are integrated, is formed. At that time, in a case where the three portions are simply abutted against one another at an end portion, the strengths of joint parts of the portions may be insufficient. Thus, a part of the clear portion is often laminated on the red portion and the amber portion. The reason for using this clear plastic portion as the collecting-side resin is that even when the clear portion is laminated on the red portion and the amber portion, the color hues of the red portion and the amber portion are not changed. Consequently, the area of a part, at which the clear portion makes contact with each of the red portion and the amber portion, increases, so that the joint strength therebetween can be sufficiently ensured.
As described above, in the case that the clear plastic portion is used as the collecting-side resin, when the color of the pre-molded plastic portion is mixed with that of a region used as the clear portion, the appearance of the lens is disfigured.